Encounters with oxygen: Aerobic physiology and H₂O₂ production of Lactobacillus johnsonii

Lactic acid bacteria (LAB) are intimately entwined with human life. They ferment several key food products in our diets and they reside on the mucosal surfaces of the mouth, intestine and vagina. Administration of adequate amounts of certain LAB species has been shown to provide health benefits, such as attenuation of antibiotic-associated diarrhoea. Lactobacillus johnsonii is a LAB that is used in the food industry for such health-benefit, or probiotic effects. The functionality of L. johnsonii and other related LAB in the food industry and in the host-related environment are strongly dependent on environmental factors. Especially oxygen and carbon dioxide were found to have a major influence on metabolism, growth, gene expression, yield, and viability. This thesis addresses the consequences of exposure to these two gaseous components on L. johnsonii.